QEMU Virtual CPU support

I'm getting a crash in my KVM virtual machine:

# rr record sleep
rr: Saving execution to trace directory `/root/.local/share/rr/sleep-0'.
[FATAL /home/roc/rr/rr/src/PerfCounters.cc:136:get_cpu_microarch() errno: ENOTTY] CPU 0x660 unknown.
Aborted (core dumped)
# cat /proc/cpuinfo 
processor   : 0
vendor_id   : GenuineIntel
cpu family  : 6
model       : 6
model name  : QEMU Virtual CPU version 2.1.0
stepping    : 3
microcode   : 0x1
cpu MHz     : 2693.764
cache size  : 4096 KB
physical id : 0
siblings    : 1
core id     : 0
cpu cores   : 1
apicid      : 0
initial apicid  : 0
fpu     : yes
fpu_exception   : yes
cpuid level : 4
wp      : yes
flags       : fpu de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pse36 clflush mmx fxsr sse sse2 syscall nx lm rep_good nopl pni cx16 x2apic popcnt hypervisor lahf_lm abm
bogomips    : 5387.52
clflush size    : 64
cache_alignment : 64
address sizes   : 40 bits physical, 48 bits virtual
power management:

Start by reproducing the failure with rr record sleep on the reported QEMU Virtual CPU, then inspect rr/src/PerfCounters.cc around get_cpu_microarch() at line 136. Compare the reported CPU identifier with the microarchitecture handling there. Done means recording no longer aborts for this CPU, with a regression test if the existing test structure supports it.